Published German patent specification No. 2 519 050 describes a rod of plastics material which is reinforced by an axial metal wire and which has a star-shaped cross section to provide longitudinal cavities. The rod is subjected to axial traction within its elastic limit, and optical fibers are inserted in the cavities while the rod is elongated by the traction. The traction is then released so that the fibers take up a degree of slack in the longitudinal cavities. However, the rod and the metal strength member have very different coefficients of elasticity under tension, and the elastic limit of common metals is too small to ensure that the optical fibers are not themselves subjected to excessive traction stress while the cable is being handled or laid. Furthermore, plastics materials tend to elongate in a manner which is partially irreversible. Thus, this prior method fails to avoid putting excessive traction stress on the optical fibers, and there is a danger of the fibers breaking.
Preferred implementations of the present invention provide a method of making an optical fiber cable in which the optical fibers have enough slack in their longitudinal grooves or cavities to ensure that they are not subjected to dangerous levels of traction stress during cable handling or laying, thus avoiding the risk of breakages.